System of motor control



A ril 15 1924. 1,490,720

E. F. w. ALEXANDERSON SYSTEM OF MOTOR CONTROL Filed Jan. 9 1922 'lnnnflrmmml- Fig. 2.

His Aitorne g.

Patented Apr. 15, 1924.

UNITED STATES PATENT oFncE.

ERNST F. W. ALEXANDERSON, OI SCHENECTADY, NEW YORK, ASSIGNOB TO GENERALELECTRIC COMPANY, CORPORATION OF NEW YORK.

SYSTEM OF MOTOR CONTROL.

Application filed January 9, 1923. Serial No. 527,815.

To all whom it may concern:

Be it known that I, ERNST F. W. ALEX ANDERSON, a citizen of the UnitedStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements in Systems ofMotor Control, of which the following is a specification.

My invention relates to the control of electric motors, and it providesimproved means whereby the motors may be started and stopped andenerally controlled in a safe, reliable and e%cient manner.

More specifically, the present invention relates to improvements of thesystem of motor control for which Benjamin W. Jones filed an applicationfor patent, Serial No. 527,840, on January 9, 1922, and which heassigned to the same assi nee as this invention. However, I would ave itunderstood that in certain of its aspects, my invention has a broaderapplication than its use in a system of the general type disclosed inthe said application for patent. The arrangements described and claimedin the said Jones application make use of the idea of controlling anelectric motor in accordance with the rate of change of a condition ofthe motor or of the motor circuit. One arrangement makes use of thebroad idea by controlling the motor in accordance with the rate ofchange of the enerated or counter-electromotive force 0 the motor whichis proportional to the speed of the motor. In another arrangement, thecontrol of the motor is in accordance with the rate of change of thecurrent taken by the motor, and in another arrangement the control is inaccordance with the rate of change of the voltage drop across anaccelerating resistor. The acceleration of the motor is governed byelectromagnetic switches of the type shown, described and claimed in theapplication for patent by Eugene R. Carichoif and Benjamin W. Jones,Serial No. 421,291, filed November 2, 1920, and assigned to the sameassignee as this invention. These switches are provided with twomagnetically independent electromagnets which jointly control a switchmember which is biased to a predetermined position, as, for

'a drop-out electromagnet. In t instance, the closed position. One ofthe electromagnets may be termed a pick-up electromagnet and the othermayl be termed e aforesaid Jones application, the pick-up electromagnetis energized to'open the switch and the drop-out electromagnet isenergized responsively to the rate of change of an operating conditionof the motor such as the rate of change of an electrical condition ofthe motor circuit, to govern the closin of the switch to thereby overnthe acce eration of the motor. 1%16 winding of the drop-outelectromagnet is energized from the secondary of a transformer, theprimary of which may either be connected across the motor armatureterminals or across one of the acceleratin resistors as a shunttransformer, or be irectly included in the motor armature circuit as aseries transformer.

In order to obtain suflioient energy from the secondary of thetransformer for the control of the closing of the switch, a fairly largetransformer. is necessary, and one of the objects of the presentinvention is to rovide an arrangement in which the transormer or othermeans for supplying a potential which varies with the rate of change ofthe selected motor operating condition may be quite small or beeliminated entirely. My invention is not necessarily limited to its usein connection with a transformer and switches of the type disclosed inthe said Carichofi and Jones application, Serial No. 421,291 but theprincip es thereof are readily explained in connection with anarrangement involving the use of a transformer and switches of thattype.

In accordance with my invention, an electric valve such as a liotron orradiotron is used to regulate su cient power to control or operate motorcontrolling means such as an electroresponsive switch, which in turncontrols the motor. A pliotron or radiotron is an'electron dischargedevice which comprises three principal elements; namely, the plate oranode, the filament or heated cathode and the grid. The late may beconnected to the positive si e of the suppl circuit for the motor, andthe filament, who must be heated to incandescence in any" suitablemanner may be connected to the negative side oi the supply circuit. Thegrid, which is ordinarily located between the plate and filament, isprovided for supplymg an electrostatic field. If this field 1s negativerelative to the filament, 1t W111 practically shut oil or quench thecurrent flowing between the plate and filament, but if the field ispositive it will augment the current flowing. If the field is neutral orzero, the current flowing will be about onehalf of the maximum currentobtainable by making the field positive. The voltage of the grid need becomparatively low in order to have either a shut off or a maximumcurrent condition. The winding of the electroresponsive motorcontrolling switch or the drop-out winding of an electrom etic switchsuch as described and claimed in the said Carichofl and Jonesapplication, Serial No. 421,291, may be connected in series with. theplate of the pliotron, and the grid is given a negative value when thecontrolling condition of the motor is constant that is, when the speedof the motor, or the motor counter-electromotive force, or the currenttaken by the motor, or the drop across an accelerating resistor, or anyother selected condition of the motor, is constant. The potential of thegrid is changed to a positive value while the selected condition of themotor is changing. Thus, the drop-out winding of the electromagneticswitch may be thereby energized while the selected condition of themotor is changing and deenergized when the condition becomes constant.

' A very small impulse is therefore necessary to energize the pliotrongrid, and this small impulse may be used to regulate sufficient power tocontrol the operation of the motor accelerating switches, or any othersuitable means for controlling the motor. The pliotron thus serves as anelectrical amplifier or intensifier for the comparatively small impulsewhich is obtained from a transformer or a condenser connected so as todeliver an impulse in accordance with the rate of change of the selectedoperating condition of the motor.

For a better understanding of my invention, reference is had to theaccompanying drawing wherein Fig. 1 shows an embodiment of the inventionemploying an electric valve or electron discharge device in connectionwith a transformer having its primary connected across the motorarmature terminals; Fig. 2 is a very simplified diagram of Fig. 1; andFig. 3 is another very simplified diagram showing an arrangementinvolving the use of a condenser instead of the transformer as in Figs.1 and 2.

Referring to the drawing, the electric motor 10 is adapted to beconnected to the source of supply 11 by means of the electromagneticline switch 12, which when closed connects the motor to the source ofsupply through a circuit including the starting resistors 13 and 14. Theelectromagnetic relays 15 and 16 are provided for controlling theclosing of the resistor electromagnetic switches or contactors 17 and18. These relays are preferably of the type disclosed in the saidCarichofli' and Jones application, Serial No. 421,291, filed November 2,1920. The relay 15 comprises a pick-up winding 19 and a drop-out winding20 which jointly and severall control the single switch member 21. herelay 16 comprises the pick-up winding 22 and the drop-out winding 23which jointly and severally control the switch member 24. The drop-outwindings 20 and 23 of these relays are controlled by means of theelectric valve or electron discharge device 25.

This electron discharge device comprises a plate 26 which is connectedto the positive side of the source of supply through the drop-outwindings 20 and 23, the filament or heated cathode 27 and the grid 28interposed between the plate 26 and the cathode 27. The cathode 27 isadapted to be heated by means of a suitable low potential source ofcurrent as indicated at 29, and this cathode is connected' to thenegative supply conductor through the comparatively low resistanceregulating resistor 30. The grid 28 is connected to the secondary of thepotential transformer 31 which has its primary connected across thearmature terminals of the electric motor 10. One terminal of thesecondary of the transformer 31 is connected to the negative supplyconductor and the other terminal is connected directly to the grid 28.The comparatively high resistance resistor 32 is connected across thesource of supply in series with the regulating resistor 30, therebyforming a potentiometer connection, so that the potential of thefilament 27 may be very accurately controlled by means of the regulatingresistor 30. The potential of the filament will be positive with respectto the grid.

As thus constructed and arranged, the operation of my invention is asfollows: In order to start the motor, the disconnecting switch 33 willfirst be closed. The pickup windings 19 and 22 of the acceleratin relays15 and 16 will thereby be energized across the source of supply toattract their respective switch members 21 and 24 and magnetically holdthese switch members in the open position. In order to start the motor,the pilot or master switch 34 will first be closed, thereby energizingthe line contactor 12 to close and connect the motor to the source ofsupply through the accelerating resistors 13 and 14. The closing of theline contactor 12 short circuits the pick-up winding 19 of the relay 15,but this relay will be held open by means of the winding 22 of the relay16 across the accelso that this relay will era-ting resistor 13 id openby the windings be magnetically he 22 and 23. l

The drop-out windings 20 and 23 of the relays will be energized throughthe electron dischar e device 25 because of the fact that the grid 28will be changed from a negative to a positive potential due to theclosing of the line contactor 12. When the line contactor 12 closes, therate of chan e of the generated potential of the motor Will be asubstantial value, and as the motor accelerates, this generated orcounter-electromotive force of the motor will gradually increase, butthe rate of increase will become less as the speed of the motor becomesconstant. The voltage induced in the secondary of the transformer willtherefore approach a zero value, and the potential of t e grid 28 willgradually change from a positive to a negative value. The currentthrough the secondar of the transformer has a path through a focalcircuit which includes the filament 27 and the resistor 30. Theprincipal effect of the grid 28 is to set up an electrostatic fieldbetween the late or anode 26 and the cathode 27 for t e purpose ofregulating the value of current through the drop-out windings 20 and 23of the controlling relays, so that when the grid potential becomes apredetermined negative value with respect to the filament 27, the valueof current through the device 25 and the drop-out windings of the relayswill be insufiicient to magnetically hold the relay 15 open. When thespeed of the motor has finally become substantially constant, theelectrostatic field set up by the grid 28 will be of a ne tive valuesuch that the current through t e electron discharge device will be verysmall and the drop-out windings of the relays will be substantiallydeenergized.

The deenergization of the drop-out winding 20 of the rela 15 willrelease the switch member 21 to rop to its normally closed position inaccordance with the bias of the spring 35, the relay 16 remaining in theopen position because of the fact that the pick-up winding 22 isenergized across the accelerating resistor 13. When the relay 15 closes,the resistor contactor 17 is closed, thereby short circuitin theaccelerating resistor 13. When this appens, the pick-up winding 22 ofthe rela 16 will be short circuited and deenergize but the drop-outwinding 23 of this relay will be energized through the electron ischargedevice to maintain the relay in its open 0- sition. It is also to benoted that the e ectromagnet associated with the pickup winding 22 willretain its holding effect for an interval of time, because it will take.a certain time interval for the magnetism of the pick-up electromagnetto decrease because of the short circuiting of its winding, in a mannerwell understood. The closing of the contactor 17 will cause the grid 28to become positive with respect to the filament 27, thereby permittinganappreciable current to pass through the electron discharge device toenergize the drop-out winding of the relay 16 to hold the switch memberof this relay in the open position. The drop-outwinding 20 of the relay15 will also be energized, but this energization will not be sufiicientto open the relay. As the motor accelerates in speed, the id 28 will setupan electrostatic field whic gradually approaches thenegative value atwhich the passage of current through the electron discharge device isquenched, thereby deenergizing the drop-out magnet 23 when the speed ofthe motor has become substantially constant. The closing of the relay 16will energize the resistor contactor 18 to close and short circuit theaccelerating resistor 14. The current passing through the drop-outwindings of the relays 15 and 16 will not be sufllcient to open theserelays after they have been closed in the manner ex lained.

y reference to Fig. 3, it will be seen that instead of the transformer31 of Fi 1 and 2, I have provided a condenser 36 or regulating theelectrostatic field set up by the grid 28. The comparatively highresistance variable resistor 37 is provided for gradually draining offthe electrostatic charge of the condenser 36 at a desired rate. Thearrangement shown in 'Fig. 3 is a very simplified diagram of thearrangement of Fig. 1 with the condenser 36 used instead of thetransformer 31. This arrangement will operate in the same manner as thatpreviously described in connection with Figs. 1 and 2. 'It is to benoted, however, .that the condenser arrangement of Fi 3 will operatemore as a timing device t an as a rateof-change device. The condenser 38may be arranged to be connected in multiple with the condenser 36 by theclosing of an auxiliary switch 39 associated with the contactor 17 forthe purpose of obtaining a greater efi'ect from the condenser at thispoint in the motor acceleration to give a time delay in the closing ofthe next contactor.

While I have shown my invention as used in connection with a system inwhich the accelerating resistors are intended to close no f selectedchanging motor operating condition, but it is applicable generally tothe control of electric motors in accordance with the rate of change ofany of the well known motor operating conditions.

If the ratio of inductance (L/R) of the transformer 31 is large, thenthe transformer will function more as a timing device than as arate-of-change device. If L/R-is small, then the transformer will haveto be lar er, but it will function more as a rate-o -change device. Theimpressed voltage on the transformer increases as a function of thespeed and the induced current will be in one direction approaching zeroonly when the motor speed has ceased to increase. This produces a resultin accordance with requirements, and the L/R factorm'ay be used'bestsuited to the work without bein otherwise restricted.

The trans ormer and electron discharge device arrangement of Fig. 1 maybe designed so as to give a control which is a combination ofrate-of-change and time functions, and the rate-of-change function maybe predetermined to be the predominating function. The condenser andelectron discharge device arrangement of Fi 3 will give a control whichhas a time unction as the major factor, but the rate-of-change and timefunctionsmay be redetermined to give an appreciable rate-o -changefunction.

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown in onlyillustrative and that the invention may be carried out' by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, 1s 2- 1. A control system for electric motors comprising motorcontrolling means, and an electron dischar e device connected to besubjected to a sefiected motor operating condition and connected toregulate the supply of energy to the said motor controlling means inaccordance with the selected motor operating condition.

2. A control system for electric motors comprising an electron dischargedevice having a grid connected to have a potential which varies with aselected motor operating condition, and motor controlling means underthe control of the said device.

3. A control system for electric motors comprising motor controllingmeans, an electron discharge device for controlling the said means, thesaid device having a grid, a heated cathode and an anode, andconnections whereby the potential of the grid of 5. A contro system forelectric motors 1 comprising an electron discharge device, meanscontrolled thereby for controlling the motor, and connections wherebythe said device ,amplifies'an operatin condition of the motor to controlthe sai means.

6. A control system for electric motors comprising an electron dischargedevice,

means controlled thereby for controlling the motor, and connectionswhereby the said device controls the said means in accordance with therate Qfchange of the-counter-electromotive force of the motor.

7. A control system for electric motors comprising an electron dischargedevice, electroresponsive means controlled thereby for controlling themotor, and connections whereby the said device varies the supply ofenergy to the said electroresponsive means in accordance with the rateof change of an electrical condition of the motor.

8. A control system for electric motors comprising an electron dischargedevice, electroresponsive switch mechanism controlled thereby forcontrolling the motor, and connections whereb the said device regulatesthe current supp ied to the said electroresponsive switch mechanism inaccordance with the rate of change of an operating condition of themotor.

9. A control system for electric motors comprising motor controllingmeans, an electron discharge device having a grid, means connected to imress on the said grid an electrical potential which varies responsivelyto the rate of change of an operating condition of the motor, andconnections whereby the said motor controlling means.

is energized through the said device and the supply of energy to thesaid means in varied lIlfiCCOI'dfi-HGO with the potential of the saidgr1 10. A control system for electric motors comprising electromagneticswitch mechanism for controlling the motor, an electron discharge devicehaving a grid, means connected to impress on the said grid an electricalpotential which varies responsively to the rate of change of thecounter-electrometive force of the motor, and connections whereb thesaid switch mechanism is energizedt rough the said device and the supplyof energy to operate the said switch mechanism is varied in accordancewith the potential of the said grid.

11. A control 5 stem for electric motors comprising an e ectrondischarge device, means controlled thereby for controllin the motor, andconnections between the sai de vice andthe motor to be controlledwhereby the said device controls the said means in trolled thereby forcontrolling accordance with a time function and the "rate of change ofan operating condition of the motor.

12. A control system for electric motors comprising an e ectrondischarge device, electroresponsive switch mechanism conthe motor, andconnections between the sa1d device and the motor to be controlledwhereb the said device regulates the current supplied to theelectroresponsive switch mechanism in accordance with a time functionand in accordanoe with the rate of change of an operating condition ofthe motor.

13. A control system for electric motors comprising electroma netic.switch mechanism for controlling t e motor, an electron dischargedevice having a grid, means connected to impress on t e said grid anelectrical potentialwhich varies responsively to the rate of chan e ofthe counter-electromotive force of t e motor and with a time function,and connections whereby the said switch mechanism is energized throughthe said device.

14. A control system for electric motors comprising electroma eticswitch mechanism for controlling this motor, an electron dischargedevice having a grid, a transformer electrically connected to the motorto induce a voltage in its secondary which varies with the rate ofchange of an operating condition of the motor, and connections wherebythe said 'd is connected to the secondary of the said transformer, the

said switch mechanism is energized through the said device, and thesupply of energy to operate the said switch mechanism is varied inaccordance with the potential of the said 1 15. A control system forelectric'motors comprising electroma etic switch mechanismfor'controlling t e motor,'an electron discharge device having an anode,a heated cathode and a grid, a transformer having its primary connectedacross the motor armature and its secondary connected to the said gridto impress thereon a potential which varies responsively to the rate ofchange of the counter-electromotive force of the motor, the said switchmechanism being connected to a source of supply through the said cathodeand anode so t at the supply of energy to operate the said switchmechanism is varied in accordance with the potential of the said grid.

' potentia 16. A control system for electric motors comprising anelectromagnetic switch for controlling the motor, the said switch havinga switch member biased to one position and two windings whichsuccessively control the operation of the switch, one of said windingsfor governing the operation of the switch member to a second positionand the second of said windings for governing the return of the switchmember to its biased position, and an electric valve connected toregulate the current supplied to the said second winding inaccordancewith the rate of change of an operating condition of themotor.

17. A control system for electric motors comprising an electromagneticswitch for controlling the motor the said switch having a switch memberbiased to one position and two windings which successively control theoperation of the switch, one of said vwindings for governing theoperation of the switch member to a second position and the.

second of said windings for governing the return of the switch member toits biased position, an electron discharge device havmg a grid connectedto have a potential which varies with a selected motor operatingcondition, and connections whereby the supply of current to the saidsecond winding is governed in accordance with the of the said grid.

18. A control system for electric motors comprising an electromagneticswitch for controlling the motor the said switch having a. switch memberbiased to one position and two windings which successively control theoperation of the switch, one of said windings for governing theoperation of the switch member to a second position and the second ofsaid windings for governing the return of the switch member to itsblased position, an electron discharge device havmg a grid, a heatedcathode and an anode, means for impressing a potential on the said gridwhich varies in accordance with i a selected motor operating condition,and connections whereby the said second windmg is connected to a sourceof supply one position and, two windings for successively controllingthe operation of the switch, one of said windings for governing the oration of the switch member to a secon position and the secondof saidwind ings for governing the. return of the switch member to its biasedposition, an electron" discharge device having a grid, a heateddelivered to the said second cathode and an anode, a transformer havingits primary connected across the motor armature and its secondaryconnected to the said grid for impressing a potential on the said gridwhich varies in accordance with the rate of chan e of thecounter-electromotive force of t e motor, and connections whereby thesaid second winding is connected to a source of sup 1y through thecathode and node of san theenergy, delivered'to the said second windmgis under the control of the potential of said grid.

device so that.

In witness-whereof, I hsve hereunto my hand this 7th, do of Jenna. 1929.Y

XLEXAND Rs0N.

5 ERNST F: W..

